Modern analytical instruments and equipment applied in high pressure liquid systems have inherently become more complex. This axiom also applies to tube connectivity and interchangeability where instrument designers are challenged to connect fluid and gas lines easily, reliably and inexpensively.
Typically, two alternative fluid connections to these fluid flows, such as High Pressure Liquid Chromatography (HPLC), Flow Injection Analysis (FIA) and Total Organic Carbon (TOC), to name a few, have been employed. The first approach is to modify the tubing (such as flaring the end of the tube) to enable a threaded nut to drive a washer or o-ring device down on the flare which in turn pushes on a flat-bottom receiving section of the device to make a seal.
The next approach, and perhaps the more common approach, is to add a compression ferrule between the tube and the device receiver which allows a threaded nut to drive the ferrule and tube together and against a conical receiving section of the device to create a seal. Generally, compression ferrules are employed as reliable and simple fluid line connections in high pressure liquid systems such as High Pressure Liquid Chromatography (HPLC) and DNA sequencing systems. These compression ferrules are relatively small conical structures which cooperate with one or two-piece tube fittings to form fluid-tight connections to the instrument tubing. Typical of such compression ferrules fittings are the RHEFLEX® Precision, Twist-Free and Flangeless PEEK Fittings by Rheodyne, L. P. of Rohnert Park, Calif.
To match the chemical inertness of the components with the demands of the chemistry applied within the analytical instrument, various materials are utilized for the tubing, nuts, washers, o-rings and ferrules. These include PEEK, Stainless Steel, Kel-F, etc.
Additionally, various thread designs have been used in an attempt to minimize the size of the device receiver (stator in the case of an injection valve). These include nuts with ¼–28, 10–32, M4, etc, threads. By using progressively smaller threaded fittings, manufacturers are able to reduce the size of the functioning device, as the footprint is often limited by the geography required to make tubing connections. Indeed, most manufacturers have been forced to machine complex “angles-of-approach” for the tubing connections (ports) as a way of accommodating the size of the connector (threaded nut). It should be noted that the complex machining procedures burden these devices with a high cost structure and therefore, expensive market price.
Finally, the use of individual threaded nuts for each tube greatly complicates the process of installing and removing the tubes. As tubing densities increase the impracticality of using individual threaded fittings becomes obvious.
Accordingly, as modern fluid connections increase in density, it is desirable to simplify the fluid connection with the plurality to tubes, while minimizing the overall size of the functioning device.